Field of the Invention
The invention relates to a method for operating a first energy generator in an electric power supply system to which a plurality of electric consumers and at least the first energy generator, which in particular is embodied as a regenerative energy generator, are connected via respectively one grid connection point each assigned thereto, wherein at least the first energy generator has an inverter of predetermined power rating, the AC voltage output of which is electrically connected to a first grid connection point assigned thereto, and wherein the operating control of the inverter regarding its reactive power feed and/or its reactive power draw into or out of the electric power supply system takes place depending on a continuously measured mains voltage value (NNetz).
Description of the Background Art
In the practice of public power supply, in the electric power supply system depending on the supply voltage level, which in Germany, for example, ranges from 380 kV and 110 kV as the high-voltage level, via 15 kV to 70 kV as the medium-voltage level down to 230 volts on the low-voltage level, more or less narrow limits are set by the energy providers or system operators for the current quality or voltage quality with respect to the reactive power component of the power suppliers and the power consumers, represented by the cos phi value in the phasor diagram of current and voltage.
In Germany, the permissible value of cos phi for a reactive power draw without penalty or a reactive power feed-in is 0.95. This limit setting serves to stabilize the grids in order to avoid an overvoltage, which can lead to a destruction of connected consumers, and an undervoltage, which can lead to a failure of consumers. The price serves as a counterbalance to maintain the set cos phi values. Thus a feed or a draw of reactive power outside the bandwidth stipulated by the energy generator or higher-level grid operator for the cos phi is punished by substantial fines.
A variety of installations for generating electric energy are known. Every photovoltaic plant, hereinafter also referred to as a PV plant, generates a direct current, which is converted into an alternating current by means of an inverter and, with suitable conditions, is fed into an electric power supply system. Purely electronic devices as well as electromechanical rectifiers can be used as inverters. Inverter is understood thereby to mean all of the devices that can generate an alternating current from a direct current. Thus wind energy plants generate an alternating current directly. However, this has to be adjusted to the conditions of the public supply system (energy power supply system) via a frequency converter. These frequency converters likewise comprise inverters according to the invention.
The electronic components of an inverter, just like the combination of a direct current machine with a synchronous generator as a mechanical inverter, permit the adjustment of a desired cos phi value. This occurs in most PV plants by means of a cos phi indicator, via which a fixed ratio of fed power to fed or drawn reactive power can be adjusted. Thus the control unit, e.g. is instructed to adjust each power fed into the grid at a cos phi of 0.97.
For example, from unexamined German application DE 199 61 705 A1 an inverter for a photovoltaic plant is known, by means of which a solar system can be connected to an electric power supply system and which has a control unit for the dynamic calculation of a compensation current to compensate for harmonics and reactive power in the grid. The operation of the inverter with the control unit is intended to improve the mains voltage quality in the electric power supply system.
The control unit calculates a compensation current desired value based on a measured mains voltage value. The measuring element of the mains voltage measurement is thereby arranged at that connection point at which the inverter feeds the energy into the grid.
In the case of larger and modern installations, the cos phi value is not necessarily fixedly stipulated, but can be adjusted dynamically in operation according to a diagram corresponding to FIG. 1 depending on the momentary requirements. There a cos phi value (cos φ) to be adjusted is plotted at the output of the inverter over the mains voltage. The output voltage UNetz for feeding into the grid may vary only within a range between the minimum value Umin and a maximum value Umax. The PV plant should not be operated outside this range of feeding into the grid with a cos phi of e.g., no more than 0.95, permitted by the energy supplier. Within this permitted range lies a narrower range between a minimum control voltage Uregel min and a maximum control voltage Uregel max, in which pure power without a reactive power component can be delivered to the grid. In the center of this narrow range lies the desired voltage Usoll.
The invention is now based on the concept that it can be useful for a grid operator or energy supplier to coordinate the energy generators and/or energy consumers operating in the grid with one another such that the individual installations of grid participants which can be combined administratively or in the operating control by the grid operator or energy provider in order, for example, to form a virtual power plant, are operated more unfavorably regarding the cos phi in order in the interaction with other elements overall to create more favorable conditions in her ratio of reactive power and active power and to avoid impending fines of their own to the higher-level system operators.
Thus energy providers, above all in their contractual relationship with the higher-level system operators (e.g., nuclear power plant, coal-fired power plant, etc., as energy supplier), are contractually obligated not to fall below a reactive power demand value of cos phi 0.95 in order to ensure the voltage stability in the supraregional higher-level grid. However, an import of reactive power is often necessary in the lower-level grids, in order to compensate for a voltage increase through the feed-in of solar power and wind power or to compensate for a drop in voltage due to the failure of a supply of alternatively generated energy or the start up of machines.